I would be willing to bet that the OP was using a regular poncho (which I believe from his description of the issues he had) instead of a bike specific rain cape.
+1 on needing a bike-specific rain cape. I picked one up from China on eBay for $20 including shipping. I slid the elastic handles over my handlebars and biked in a very heavy rain shower and got to work cool and dry. After years of sweating in "breahable" rain gear it was a revelation. Rain pants are a good addition, as is a mudflap on your front fender.