Concentrated batch

So I am not exactly blessed with the greatest equipment, and at least for now I'd like to hold back from buying much more.

I have heard that you can do a concentrated batch if you are using a somewhat smaller pot to boil in. So for example, I would mash the exact same amount of grains, with whatever the quantity of water I would normally mash with. Then I would sparge with enough heated water to create a boil that could fit in my pot - but smaller than the yield I am looking for. Assuming I extracted the same amount of sugars from mashing the full grain bill, I could do a boil - adding hops, sugars, and whatever else. Then, say I'm left with about 4 gallons or so of wort, I can add another gallon or a gallon and a half of water in the carboy, and the beer will turn out the same.

Is this true? Or would this beer end up being bad for some huge obvious reason that I am unaware of?

I have a 6 gallon pot for the boil, but 6 gallons is RIGHT up to the top. I'd be lucky to boil 5 gallons in it, but then it boils down to 4 or even less. Last time, I had a double boil going with some overflow, but I hate having to do that - I feel like having all the sugars from the grain in one pot, with even distribution of hops and all that is better.

Thanks!

Most likely your beer will turn out fine, there has been some discussion on how much hop utilization you get from higher gravity worts, but I don't think there has been any hard evidence to support it one way or another. Honestly I wouldn't worry too much about it, you'll still be making good beer.

If you are like me and constantly striving to make your brewers better, take copious notes from the start of your brew day to the last sample you try. Figure out what you like and what you want to improve, and then chage one thing next time your brew targeting the change you are looking for.