It also depends on the Potential of the athlete too and when they will max out. If you truly want to get your athletes on the NT then it would be more wise to go 1-position training instead of 2-position training. Also get a high trainer.
For example:
You're doing 2-position training and receiving only 70% of the max. So if you average 10 pops a season at max, then you'll only get 7 pops per season.
Your fellow countryman who are also training their NT potential players on 1-position training and receiving 100% of the max. They will receive 3 pops per season more than you.
With your guys being only 24, I'd suggest they would need at least 3-4 more seasons before having the slim chance at the NT. In 3-4 seasons, your fellow countryman would receive 9-16 more pops then you which could be the determining factor on whether your players actually make the team or not.
If you look at it as you want your athletes to make the NT by the time they are 34, your countryman would have received, in theory, 30 more pops than you.
Although 70% of the max doesn't sound bad, your chances of actually building and getting a player on the NT drops just as much since others are getting the max out of their players.