Long mast extension

Hi,

I'd like to hear your comments regarding two concerns I have when using a rather long mast extension (40-45 cm):
- situation A: Major part of the extension inside the mast. Let's assume that te mast has a constant curve characteristic. Will the extension inside the bottom of the mast spoil the performance? We' re talking about 30-40 cm alu piece that probably makes the lower part of the mast stiffer than should be.
- situation B: Using the extension at ful length, only 5-10 cm of it is inside the mast. Due to rather small conntact between the mast and extension, I think there's quite a pressure acting at the mast. Is there any risk to crack the mast?
Thanks in advance for your inputs,

G