Short gearing is a high ratio which means large mechanical advantage (5:1)
Tall gearing is a low ratio which means small mechanical advantage (2:1)
Just for reference.
Also I’m not convinced that just gearing yourself low will create more heat. Pretty sure if you assume the same speed and incline. Heat is not a function of amps. It’s a function of efficiency and power. So if I have a 1kw motor and 95% efficiency then I produce 10w of heat. Period.
(I’m ignoring iron losses here because they are dispositionally small)
The primary affect on efficiency is torque load.
And the curve looks as follows
Now look at the green line. This tells you that as a rule of thumb. The efficiency of a motor is a function of finding the right mix of torque and speed. Say You wanna hit the max efficiency and produce minimum heat. Then you’d want to gear your motor such that You operate to the left of those torque values. (To the right would be “over loaded” as Live pushed past maximum efficiency)
Now what that gearing looks like for 90kv motor at 16s. I don’t know yet.
But I’m just making a point that it’s not simply “Amps make motor hot, Ooga Ooga” 
There’s a sweet spot for a motor where the max efficiency load is less than what we want. Ideally we set things up. so that the torque/speed combo is right at cruising speed. Say 25mph.
Tldr takeaway is here :
Now say we’re talking 90kv vs 180kv (cause it’s an easy ratio) I’m pretty sure that if this graph is a 180kv. And sa your gearing is on that sweet spot. Then a 90kv would move the peak to the right (more efficient at higher torque) by 2x. And You could effectively halve your ratio (say from 1:4 to 1:2) and maintain the same efficiency.