center slot port length with kerf

[stipek]

box depth is 20" internal. Calculated desired port length is 22". This makes the physical port length 16.25" according to torres calc. which gives a tuning freq. of 36.57 hz. Port is 5" wide and 14" high in the center of the box for 2 12" subs with port facing back and the subs mounted up. If this were just a square port that would make L1 15" and L2 1 1/4" using 3/4" MDF. However, I want to kerf the port outlet which will be approx. a 5" radius.

So my question is do I then have to add 5" to the L2 to make up for the lose on the L1 to maintain desired tuning freq?

I was told when the outlet is kerfed the port does not actually start until the "straight" part of it which will then be approx. 5" towards the inside of the box.

I also would like to divert the air down the port by putting a couple 45's or a short diverter piece on the back wall in the center of the port.

If I do this, how long should that piece be? I don't want to choke/resist the air flow as this will be decreasing the 5" width of the port at that point. Perhaps I could also 45 the L bend to maintain the 5" width and then the L would become more of a hook.