Spot Check, the right way to use it?

Question

So, I've hit a problem with my current group regarding Spot.

The PCs were walking along a road where bandits have set up an ambush. They were about 150 feet away and it was the first occasion they could've seen the ambush (line of sight and stuff). They rolled okay and were 1 or 2 points below the DC. That got me thinking "if they were 20 feet closer or so, they would have spotted the ambush"... why did I ask for Spot 150 feet away? Why not 100? Why not both?

I feel that asking for new spot checks every 10 feet would weaken the hiding party, but you can see stuff better when you are closer, not Rolling spot again would weaken the "seeing" party (and with a -15 on the roll, they already are gimped enough)

BTW, the way I handled it was: I kept the value of the spotter, and as the penalty for distance went down enough for the DC to be beaten by the spot roll, I made a new spot roll in secret for the spotter, which he again failed by like 2 points, and I redid it... and it failed poorly so they got ambushed after all.

How should I have played that scene according to rules and common sense? (that last sentence... I have no clue how to write properly, sorry)

Answer 1

You might consider using the "Encounter distance" rules found in http://www.d20srd.org/srd/wilderness.htm and the DMG to determine the initial place at which Spot checks occur. It's going to vary by terrain of course (there's a header there entitled "Stealth and Detection in a Forest" that it seems that I can't link to directly but which might point you in the right direction and is echoed in subsequent 'terrain' sections). It's also going to vary by topography, as mentioned in that part of the SRD.

Not RAW but you might consider having both sides make Spot checks at the above "maximum encounter distance" and then have the "winning" side notice as soon as the groups come to a distance small enough that the penalty for distance no longer causes the Spot check to fail. If that makes sense. So both sides roll Spot checks; one of the groups misses by just 1; as soon as the groups are 10' closer, then that group succeeds and the encounter begins.