Methods used to determine calling ranges

[holdem17]

After practicing bubble play on some bubble trainers and messing around with SNGPT I have become decent at bubble decisions. But these decisions are assuming you know the exact range of the opponents. Since this variable is a huge factor in push/fold decisions, I am curious as to how everyone goes about putting villains on calling ranges. What default calling ranges you use on unknowns. I know there are countless scenarios and variables that factor in but I am curious about peoples thoughts on this.

How much do calling ranges tighten or loosen:

as buyins go up?
as the number of pushes you make go up?

there are a number of other questions to add here...

Also another aspect that I have been thinking about is how limpers affect push/fold