You can read sometimes that there are just a limited amount of visitors available, each day. Similar to the Galapagos at Equador.
In my eyes more advertising than an real issue for travellers, far I know - but you never know.
We didnt try to use a custom tour, did it similar to cheldon, book train & entry at the day before - which was amazing expensive at 2015.
Probably it makes sence to check online if there are overbookings visible:
https://incarail.com/
https://pax3.perurail.com/ecommerce/www/
You can choose the exact time of the train departure/arrival, "most like daytime" may be sold out sooner...
Check prices when you are there. You probably can get discounts, combos, specially when travelling together with kids.
It is a big business & ripp off & overrated location - because the country did offers so much more, and most of it completely free of charge.
Your bucks will help there. Will helps probably more if you are doing overlanding, use restaurants, bars, loundrys, guesthouse, campsites - not just at the tourists hyper hotspots.
Here is my (daily written) diary about that day:
Adventure-Overland: Machu Picchu
Surfy