If the ratio is 1, you don't want that to change much.
When it's 0.5 we might want the ratio to go up to somewhere like 0.65 instead.
So, what we can do is to take the difference between 1 and the current ratio, and increase it by a little bit.
var ratioFactor = 0.3;
var ratio = (wRatio + hRatio) / 2;
ratio += (1 - ratio) * ratioFactor;
So, if the ratio starts out as being 1, 1-ratio is 0, so there is no change there.
If the ratio is 0.8, it will be 0.2 that is multiplied by 0.3, which add 0.06 on to is, resulting in a slightly larger ratio of 0.86
If the ratio is 0.5, there will be 0.5*0.3 added on to it, that being 0.15, so the ratio will end up being 0.65
Here's a table to summarise the increase in the ratio, where the ratio brought 30% closer towards 1
I don't have Chrome TV to test with, so you might need the effect to be stronger (increase it from 30% to something larger) or you might need the complete opposite to occur, for the zooming effect to become weaker, in which case you can use a negative zoom factor.