That's strange. I've never seen an insurance co make a difference
between M20's. My open policy is 500 TT 100 retract and 25 in M20. As
your time goes up, and your rate goes down, the open pilot goes up.
When I bought my Mooney I had some time in a C model and my partner had
2 hours in a J 5 years prior. They credited that to us and we were good
to go w/o any F model instruction.

-Robert