L * W * H = cubic inches. There are 231 cubic inches in a gallon. I don't know the dimensions of your 80 Gallon display so here is an easy ballpark way to estimate. Figure out how far below the surface your return lines in the display are. (How far the water will drop in the display until the siphon is broken) Let's say that your 80 gal display will drop 2 inches until the siphon is broken. (Again this is ballpark) A 40 gal sump/fuge would then need double that amount to hold the same amount of water so you would have to leave 4 inches of space at the top of you sump/fuge. You have a 30 gal sump/fuge so you would probably need to leave in the neighborhood of 5 inches at the top. For the actual amount of space that you need to leave use the formula above where H = the number of inches the display will drop to break siphon. Then apply the same formula to your sump to see how many inches you need to leave.
ThaNgBom told you correctly on your baffles. The baffles closet to the pump do not set the water level and water volume in the return section, the outside baffles that separate your return section from the skimmer area and the fuge area are the ones that set the level. So as suggested I would cut down the length of the inside baffles so that the water has less distance to fall into your return chamber therefore creating less bubbles.
I am assuming that your sump’s dimensions are 36*16*12. Here is how to calculate you return chamber water volume. 14 * (16 - 5) * 12 = 1848 cubic inches. 1848 / 231 = 8 gallons in your return chamber. The (16 - 5) calc is the total height of your sump minus the area of space that you need to leave for a power outage with the ballpark figure that I came up with as 5 inches.
Also your calculations don't add up to me. You say that the length of your 30 gal sump/fuge tank is 36 inches. You have the compartments broken down into 3 sections that measure 14 inches, 6 inches, and 12 inches for a total of 32 inches. That leaves 4 inches for your two sets of baffles which is not enough space. In my opinion you need at least 2 inches in between each baffle which means that you need 4 inches (plus width of the material used to make the baffles themselves) for each of the two sets of baffles that you have. So that means that you need to allow for about 9 to 10 inches of space for your baffles.
Hope this helps