I am in the same boat as you OP, as I prefer to use the natural terrain to modulate my interval efforts but, at the same time, have wished there was more data out there on interval spacing, and if anyone is aware of some, it would be great if they would chime in.
Having said that, my own research has turned up a range of recommendations. Joe Friel and many other more traditional endurance racing coaches often reccomend a 1:2 work:rest interval. The idea here is that by ensuring a reasonable amount of rest, you prevent the intensity from dropping too much on the later intervals preserving the "quality" of the workout. I have seen Friel Q&As and when asked about lowering the length of the rest intervals he said something to the effect of that it would increase the intensity/stress of the workout, and he compared its effect to doing longer work intervals, or doing higher intensity work intervals, or doing more work intervals. The frustrating thing though, is that I have not seen him, or anyone else, come up with any data comparing those various intensity modulators directly. By extension, increasing the length of your rest intervals to 1:4-1:12 as you are inquiring about, would do the opposite, so to get the same aggregate training stress, you would, at the very least, want to increase the length, intensity, or number of intervals you do. The thing is, "aggregate training stress" is a very imprecise measure, and as far as I know, even if you lower the stress by increasing the rest, but increase it through more intensity or longer intervals, there is no data on if you will come out in the same place in terms of fitness.
On the flip side, there are the Tabata style HIIT advocates who suggest super short rest times. For example, a classic Tabata workout is 30sec of 100% max work, with 10sec rest, so a 3:1 work:rest ratio, repeated for a total workout length of around 4 minutes. The idea behind this is that the rest periods are short enough to prevent anywhere close to full recovery between work intervals, which increases the stress hugely, but are long enough to allow you to still go hard(er) during the work intervals, preventing it from becoming simply one 4 minute steady state effort.
My personal suggestions, at least until better data comes along, are as follows. If you believe in the principal of training specificity (that your training efforts should mirror your racing efforts, in order to force the most relevant adaptations to racing), then think about how your race efforts tend to flow. If your races are hard 5 min hills, followed by a 2.5min descent, and then hard on the flat, then your idea of extended rest intervals may be suboptimal, and instead you should do those TT style intervals on the flats between hills too. This will also be more efficient in terms of total time (which you do state is limited) in that you can get an equal amount of training stress packed into a much shorter time period.
Gotta run, but regarding peaking, remember that if you chart fitness and fatigue, they tend to move inversely. The more training you do in a block of time, the fitter you get, but the more fatigued you get too. If you chart them, you will find that a short taper of a week or so will allow fatigue to reduce while preserving most of your fitness. When the two lines cross, THAT is your peak, even if your total theoretical fitness is slightly lower than at the beginning of the taper.