Once again, many thanks for the responses and encouragement.

A few things in response.

KJs vs a 5% PFR is not a hand you want to be playing 100bb deep.
Firstly, I should start with why I played KJ. To be honest, I'm not sure. It might have been an earlier hand or I was trying to play around with ranges but either way I doubt I would play those cards today from that position and it is good to see that is what you all advise. At least I am getting that right.

Now, for Pokerstove. I've seen other people doing that same trick of just putting in a percentage and then using the hand range that results and they always get told off so I was expecting to get called on that. The problem I had is that 5% isn't very much. Each additional combo that you add to the range increases the percentage by quite a bit. There also seems to be two opinions on that, one saying to reduce it further because of Villain's position, the other to increase it.
Is this a particular problem that arises when the percentage you are working with is so narrow? If we were discussing a 20% range then adding or subtracting 3% is less of a problem.

Let's a take a simple example to show you what's wrong with your logic. Take an opponent whose range preflop is A2+. So preflop, what you call the bottom of his range is A2. Now comes the flop AA2. After this flop, do you still think A2 is the bottom of his range? No way. It's now the very top of his range!
and
And his "bottom range" on the flop isn't his bottom PREFLOP range. So he's definitely betting 99 here in most cases and probably 88 as well. You have to adjust with each street.
I think I see what you mean, and I hadn't thought about that. I'll try and remember that for next time.

I'll have another go with another hand that has a bit more action in it and see how it goes.