Town have used the same starting XI for five matches in a row in all competitions, in which the side have discovered impressive consistency.
Cotterill admitted 'the challenge' is for his back-up options – as well as any new arrivals this month – to show they can force their way into the boss' starting plans.
But while the Shrews chief acknowledged the difficulty in breaking up a side whose familiarity has achieved improved results, he admitted the same 11 players will be unable to continue starting every match with a busy period of midweek fixtures on the horizon.
"That's the challenge – that's where it is," said Cotterill. "I want those difficult decisions.
"It's upsetting for the boys when they're left out, but if you look at us six or eight weeks ago, we probably had two subs.
"What I mean by that is we had a bench full of under-18s, that was really tough on them, a great experience for them – and they come in and train with us and we love those young kids with us – but it's a bit too much of an ask for all of them.
"We've one or two in Charlie (Caton) and Tom (Bloxham) involved in the first team but we can't have a team full."
Cotterill decided against making a substitution in Saturday's 0-0 draw at Crewe, where Town were backed by almost 1,500 fans as the support rallied around improving Salop once more.
The manager said of that decision and the supporters' involvement: "Maybe that is the case (of a connection growing), maybe, I don't want to get too ahead of myself with that."
"I think they're starting to see a team develop, which is why it's very difficult at the moment to make a substitution, because everyone knows what the next man is doing at the moment.
"I would've liked to have made a sub or two, but at the end we're still the strongest team and sometimes by making substitutions you can actually upset your rhythm and put yourself on the back foot.
"I see managers make subs in the 80th minute and I think it's just for the sake of making a substitution.
"I only believe in making a substitution if it's absolutely glaringly obvious I need to make that change. I didn't see it on Saturday."