100% this. It’s now going on what…2 days? 3 days? If I was truly worried sick about a situation my horse was in you better believe I would be sending a text or calling the BO. Waiting for the “right moment” to address something that is so concerning to you…I have to believe it’s not that big of a concern. If there are others around, you pull the BO to the side and ask them to step away for a minute as you have a couple questions you’d like to address privately.
The longer you wait, the goofier you end up looking too…“BO…I noticed 5 days ago my horse was out with more horses than you told me he would be, why is that?” If you are going to ask something, just ask it! If you did that as soon as you noticed the issue, BO could have responded that it was A) a mistake and it would be taken care of or B) something else. If it were B), that’s your opening to say he doesn’t seem to be able to eat his share of hay and ask if this is normal for that pasture group when integrating a new horse in or if there is something else that can be arranged.
This situation may well resolve itself in the meantime.
Editing to add - You and only you are your horses advocate. If you board, that makes it even more important. If you are only able to be out on weekends, I would put a priority on a place that has a stellar care reputation and a communicative BO/BM.
My horse is a VERY easy keeper and laminitis risk. I have been very clear about his/my needs when moving barns; he gets a mash which I make as easy as possible, he has an auto feeder which I handle unless Im on vacation, and he has been reactive to vaccines in the past so I need to be able to check him around the clock after vaccination. That is the big up front stuff. When it comes to the day to day, I am very clear about when he needs to start wearing his grazing muzzle. Current barn was close to out of first cutting this week; my gelding put on weight with second cutting so I was clear he still needed to be on first cut and that I would get some if needed. BO took care of it herself. It’s important to develop working relationships with people that take care of your horse because it’s never smooth sailing for long if you board in my experience; and I don’t mean that as a reason to cut and run, its being able to functionally address those concerns along the way.