What balance pitfalls result from this house rule regarding levitating creatures?

Question

My table is considering the following house rule:

A creature suspended above the ground and unable to move on its own (e.g., under the effect of the levitate spell) is especially susceptible to forces that would push or pull it. When you successfully target a suspended creature with an effect that would move it, you can choose to move it an additional number of feet equal to 5 times your relevant ability modifier (e.g., your Strength modifier if you shoved the creature with a special melee attack, or your spellcasting ability modifier if you used a magical effect, such as the gust spell or the shove effect of the Telekinetic feat). The additional movement must be in the same direction as the normal movement caused by the effect you used.

A creature with a flying speed is not affected by this rule.

The logic here should be obvious -- a creature hanging in mid-air, with no ability whatsoever to stop itself from being moved, should be easy to move. But what are the implications of such a house rule from a balance standpoint? Are we setting ourselves up for headaches?

(For context: this might seem like a corner case, but we're playing a heavily psionics-themed campaign, and so maximizing players' opportunities to embody the tropes of telekinesis even at low levels is important. It isn't inconceivable that someone else in a similarly-themed campaign might have similar ideas.)

Answer 1

Specifically. The way you have worded the ability, it works too broadly.

A creature suspended above the ground and unable to move on its own

This would for example, describe a creature under the effects of telekinesis. Even though the description of the spell clearly indicates the target is being held tight in mid air (hence restrained).

Fixing that. The particularly troublesome interactions would be any ability which easily allowed forced movement. A Genie warlock with crusher, grasp of hadar, repelling blast, and +5 modifier could move a target 5+25(crusher), +10+25(grasp), +10+25(repel), +10+25(repel) feet with their two blasts. At level 11, just repelling blast is going to be over 100 ft of forced movement (well, until it knocks them out of range of the spell anyways). I prefer yanking them toward you, then launching them 30ft up with crusher, then launching another 70 ft up with the repelling blasts ending them 100ft in the air. A spell sniper / eldritch spear warlock might be able to float a target out of their range of any attacks and slowly plink them off or just let them fall.

Even without such crazy optimization, just the crusher feat would allow you to uppercut someone in the air 30 ft (and then the person can drop concentration) to deal an extra 3d6 and knock the target prone (for advantage on follow up melee attacks).

Environmental hazards are always a concern, however with such powerful forced movement abilities, fighting within 50 feet of a pit is almost certainly going to result in a fall.

But I think most of these concerns are rather the POINT of the rule rather than a drawback. If you let people play pinball with floating targets, they can play pinball with floating targets.

I would probably instead of being a formula which favored short distance moves so much, instead make it allow any forced movement to be doubled. Simplifies it and benefits short and long forced movements a proportionately equal amount.