However if you place it in one corner of your house and install a reflector with a 90-degree coverage angle you should be able to increase your signal strength

However if you place it in one corner of your house and install a reflector with a 90-degree coverage angle you should be able to increase your signal strength up to ~4-fold with a perfect reflector as you're 1/4 your coverage area. Realistically getting a 50% increase in strength is great. Using materials like aluminium or copper would greatly increase the performance of your reflector. If you by chance had a copper mesh, it would kick the tin foil a mile. I personally have access to sheet aluminium so if I were ever to build one of these I'd definitely be making it from that and not foil. (IIRC reflectivity in metals is improved with thickness, with these tin foil reflectors you're probably still getting a strong enough signal at close range from the side of the reflector you don't want signal.