Right now there is not "Half-feats" available to take at 1st level.
One reason for this might be that you cannot combine the floating +2 ASI with +1 ASI from the feat and start with an 18 in your primary ability.
What if there is a rule that, if you take a half-feat as your 1st level feat option, you MUST take +1/+1/+1 ASI option.
that way, you max in any ability would be limited again to 17 and you would need your 4th level feat to be a half feat again. to have 18 in your ability.
At your own table, you can do it more simply, by saying, "You may take any feat you want, but I will not accept any characters with an 18 in their primary stat at 1st level."
Or, you can say, "Screw it, go ahead and take an 18 as your primary stat."
The official rules are designed as they are to influence play on broad average. Overall, the designers think it is better to start with slightly lower stats, and they feel it worthwhile to influence play on broad average in this way. You, yourself, don't need to go through gyrations to continue to enforce it at your table.