Hi Dimitri ,
As a ruler of thumb, the biceps and forearms cover strips size is around 1,5 cms. You should leave 0.75 cms of the ridge (red line) and if there's no ridge in the opposite side you should cut symmetrically and make the adjustment with the other half (the inner one you have) .
Bellow you can see some reference images and you can take a look to the Gallery Section HERE
References of the original RS suit
Hope this can help and before any cut , if you have any doubt please reach us