Bottom line up front, it’s likely that doubling or tripling your outlets on your existing mains will help, but each situation is site specific - more below.

To analyze your system, we have to understand the concept of drainage coefficient.  A drainage coefficient really specifies the amount of a steady-state rainfall your system could maintain removing while keeping the water table constant.  So if it drizzled all day and night at a steady rate of 3/4”, a system designed for a 3/4” DC could maintain the previous water table in the soil, broadly speaking.  But we know it doesn’t rain like that much in the Midwest, we get storm systems where the rainfall quickly ramps up, hammers us, then slowly tails off.  A lognormal distribution.  But it is fair to say that the DC gives us a more or less linear measurement to use for comparisons.

First, your unrestricted drainage coefficient is a function of tile depth, spacing, and soil physical properties like Ksat, etc.  If you halve you spacing (split the middles) you will quadruple your existing DC.  So the relationship is 1/(spacing) ^2, and if you go to 1/(1/2 spacing) squared you see that your DC increases 4x.

Then you look at lateral spacing, slope, and length to determine the maximum length of, say, 4” you can install before needing to jump up to 5” in that single lateral run to fully utilize the ability of the soil water to get into the tile.  You can use those Prinsco calculators for that if you know your slope, which you can usually estimate from a LiDAR or other topo map.  The slope that actually moves the water is the grade of the water table, which typically assume is about the same as the surface slope, and that is typically a pretty fair assumption in fairly flat areas.  If your lateral size is a restriction, about the only reasonable thing you can do is split the middles, at least partway, to make the drainage area served by the lateral smaller.

Third, you look at your main capacity.  When the soil is completely flooded/saturated water will flow into the tile at a rate up to 4x the normal flow rate or even more, IIRC.  So if you are more prone to surface flooding/inundation, increasing your main DC’s to a factor that is 25-50% higher than your lateral system may be a good investment. In your case, you can do this with more outlets.  

Fourth, you look at your receiving stream.  If the tile outlets are submerged when it rains and stay submerged for some time after the rain, your water table slope is NOT the slope of the land surface because the water table at the outlet is maybe 5’ above the outlet.  In this your system DC goes towards zero and you either back up the entire system until the ditch drains, or your get surface seeps if you have a concave face on the slope of your field (hillside seeps).  One can address these issues by improving the capacity of the receiving streams - dredge the ditch, drainage district, etc.

Then you iterate until you run out of money or get the desired drainage capacity.