The Nature of RoleMaster
Probably the main thing to consider is the very reason why there are dice involved in any RPG and why realities are abstracted away from us using granular calculations and tables. We are allowing for a certain amount of play (or freedom) for our characters and NPCs to act and react outside of our control.
By its nature, Rolemaster is very digital, lending to this abstraction nicely. By abstracting away reality to this degree we can make calculations and results far more simple and much faster. Calculations rely on very stepped or fixed values to obtain results quickly (and that's really the answer - speed of calculation; it's easier to remember set numbers).
For instance, the bonuses for firing a long bow at different distances:
There's no smoothing of the process - if you fire a bow at someone 10 foot away you get a bonus of +20; if you fire a bow at someone 11 foot away you get nothing.
If you are to remain a purist, such structure should be adhered to, even with the likes of the Sudden Light spell. To that end, all light within the affected radius should remain constant and pure, affecting every creature irrespective of their orientation or position within the radius, even to the point that, should their feet be within the radius, you have to accept that the rest of their body is, also (i.e. their eyes, too). If you start adding reality to the process everything starts to breakdown.
I did try to introduce smoothing at one point but the calculations, though straightforward, were a pain to implement each time.
One point of note here is that simple effects can be added, such as applying a graded critical to ball attacks. For instance, if the highest crit at the centre is an E, then decreasing every fifth of the distance as you move away from the origin, the outside of the ball becomes an A crit. This lends a bit more realism but also takes more time to work out. Situational positioning needs to be taken into account for every person in the area of the ball.
Such a rule could also be applied to the Sudden Light spell, basing the spell attack on the distance from the centre and the initial BAR. Basically, the BAR would diminish the closer to the edge of the radius.
E.g. Curafin the elf casts Sudden Light on the middle of three orcs standing next to each other. The centre orc (A) receives the full blast of the spell and must resist the BAR of 92 (good roll!) that Curafin cast. The orc to the left (B), however, is 3 foot away and receives a slight benefit from this with a BAR of: (92 ÷ 10) x 7 (i.e. 7 foot from the edge of the circle) or 92 x 0.7 = 64.4 or 65 (we'll give Curafin the benefit of the doubt). The Orc on the right (C), however, is only 2 foot away from the edge of the circle, giving a modified BAR of: 92 x 0.2 = 18.4 (19).
Even using this method, though, I haven't taken into account the orientation of the orcs. Taking this into account you would then need to introduce an orientation calculation into the mix. Bearing in mind that the maximum rotation would be 180° we could use a similar calculation: (BAR ÷ 180) x orientation°.
E.g. One of the orcs (C) Curafin attacked was looking directly at the orc that Sudden Light was cast on, therefore receiving no modification against the base attack. The other was turned at 110° to the light, receiving a modification of: (92 ÷ 180) x 110 = 56.2 (57).
To take this a stage further we could combine the calculations as an average (not the best way, I know), but...
E.g. Orc C - ((92 x 0.2) + ((92 ÷ 180) x 110)) ÷ 2 = 37.3 (38)
Going back to the nature of RoleMaster...
So, even though one of our orcs may have been oriented away from the target of the spell, we also have to consider that they may have turned their heads to look at the target. Everything is random in this respect, unless we're being railroaded (but then why not just set the orcs that bit further apart so that they can't be affected?). This brings the point of the resistance roll and spell failure - those within the radius receive a chance to resist the spell, and there is a chance that they might, no matter how high the BAR.