So I have found that you can use the attack ground instruction ("T") to estimate distance above the selected unit's maximum range. Below the maximum range it does not display the range. That is a pain if you want to be just beyond the of a particular enemy unit. Do you just have to guess that? Or am I missing something?

Use artillery,preferably mortars because they are closer to the front.That is the only way to measure distance that I know,and also notice that line you get by using fire on position option is split into smaller ones,that can also help you in estimating when will you be able to pierce enemy armor but that is usually highlighted when you order your unit to attack enemy.

Yeah this is annoying too... Only workaround I find is to find a unit with a short range like an MMG (you could turn a tank's main gun off and then check range perhaps) or to line one up with a LOS obstruction and check it that way. Shame the numbers can't just always be there...

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AKA General Veers

This is what I do too. I wish there was some kind of option for range finding, similar to fire on position except not.