It doesn't look like you do any sort of VO2 work. 2x20's and sub-threshold work will help 'push up' your threshold whereas V02 work will help 'pull it up'. Consider throwing in a set of 5x5 minute or two sets of 4x3 minute intervals every week or two. Your 5x1 minute intervals are good for working your anaerobic work capacity and will help (slightly) with 20 minute wattage, but it will have a minimal affect on your aerobic fitness and FTP. You probably saw increases in 20 minute wattage because you were using a higher % of your anaerobic capacity.