Having the return in the bottom is fine, as long as it doesn't shoot under the baffles. Then it won't let the oil have a slow draw and not let the hot oil go to the top. Hard to explain, but you want to make sure all the oil is being circulated. I had a splitter built by a guy that makes a lot of "commercial splitters" but his tank designed sucked and I had oil temps all over the place. In the corners of my tank, where the temp gauge was mounted, was 20 degrees difference. I had an oil cooler with a 140 degree temp switch, how I found out the difference (it turned on and the temp gauge read 160). You don't have to work hard or fast. When you aren't doing anything, oil is still circulating through the system. My new splitter, that's how I raise the temp, just let it run. I have a 28gpm pump and the first valve is a 30gpm valve with power beyond to a dual spool, 25gpm valve bank (used for the 4 way and log lift) which creates heat. I run a good oil cooler to maintain my 30+ gallon tank. In 89 degree weather, my cooler was cooling all my oil from 135 down to 126 and then shutting off till the temps raised again.
It's all in the design of the system. A million ways to do it.