A post if the image would be helpful. What temp was your developer at the time? Did you try a different batch or kind of paper?
I would suggest using a heavier dilution of chems as well. Let's see, what do I use... I think I use 100cc A and 100 cc B to a liter of water. Quite a bit more than you, and my temps are around 90F for developing.
Why don't you give that a try and see what you get. I would also suggest having a couple different papers to try.
Letting the bulb cool of would do little, except make your consistency go out the window. And yes, it would be darker, but I don't believe you are on the right track with that.
Highlight detail is controlled via the exposure however, so you may need to go longer. I wouldn't know what your light sources is, what the f-stop you use is, how bright the source is on the paper, but on my systems, a minute or two is typical for exposure and I have sat with an image in the soup close to your dilution for 25 minutes rocking that thing back and forth until I almost went crazy. So you see there are several variables here as well.
Best of luck. Let us see the images, that will help.