By the way, Les McLean's procedure is great, but I find that if you have an image that is inherently light and low in contrast, then it works better if you reverse the order. Start first with the high contrast filter and adjust for the shadows, then when that is dialed in, add the low contrast filter test strip.
Here is another thing to try once you get a usable straight print of a normal negative.
Say you have that print in hand and say it was made using the 0 filter for seven seconds and the 5 filter for four seconds.
Now make two more prints without changing anything. The first additional print will be made just using the 0 filter for the same seven seconds. The second additional print will be made just using the 5 filter for the same four seconds. I expect you will find it really revealing how much the printed image comes from each exposure.
Here is another thing to try once you get a usable straight print of a normal negative.
Say you have that print in hand and say it was made using the 0 filter for seven seconds and the 5 filter for four seconds.
Now make two more prints without changing anything. The first additional print will be made just using the 0 filter for the same seven seconds. The second additional print will be made just using the 5 filter for the same four seconds. I expect you will find it really revealing how much the printed image comes from each exposure.