4.5 Gallon batches, does it matter?

So for my last 2 batches, I've been using a 5 gallon carboy as my primary fermenter (I don't use a secondary). I've been topping them off with water just at the 4.5 gallon mark to make a little room for head space. I made the batches using recipes for 5 gallon batches. After losing some beer to blowoff and trub, I'm bottling a little over 4 gallons.

My question is, does it really matter that I'm using the amount the ingredients in a 5 gallon recipe for a batch that's under 5 gallons? Or should I just open my wallet and purchase a 6.5 gallon carboy the next time I'm at my LHBS?

What matters is the gravity your are trying to achieve. If you dilute up to 5 gallons or don't dilute up your OG will change... it will be higher if you don't dilute and lower if you dilute however the recipes call for a specifiy OG and if you don't dilute you will not hit it. You would have a stronger beer, which isn't nec. a bad thing, just not exactly what the recipe intended.

Matter? No, it's still beer.

A little stronger than intended but, still beer. Just don't compete with them unless you know for certain what has changed so you can choose the categories appropriately. Softwares help with this. Otherwise, just drink responsibly.

Thanks for the responses. My coffee stout worked out very nicely since I didn't use the full 5 gallons of water, but for my future batches I'll make sure to add the proper amount so they're not as strong.