Fin Tuning Formula 161

[Heka]

Hello.
I ride F161 and my fins are. R19 70cm, R13M 70 cm, R13 H+ 70cm.

My measures are 180cm and 100kg.

I'm wonderin if i could shorten either R13M OR R13H+. How would the ability of the fin+board change if i cut for example 3-5 cms from the tip of fin.

I'don't use the R13H+ very often so should i try to cut it down?

I'm not going to buy a new fin and going to manage with these.