Spacing of new Hybrid Teas

I just placed an order for a bunch of new Hybrid Teas each within 3 -
5 feet of growth, but a rather large amount of variety in terms of
color etc.  I made the assumption that 3 feet of spacing for each
plant is sufficient.  Although I have heard about another approach
that you should add up the heights  of 2 adjacent plants and then
divide that in half to get the proper spacing.

My question is - can I just go with my 3 foot average and be safe?

What does everyone else do?