Startup is a time when many viruses are loaded so it is advisable it runs early to prevent viruses loading into memory, etc.
What is your sensitivity level for Standard Shield ?
Normal is the default and provides a compromise between protection and performance.
Can you give us some idea of the performance of your system, CPU, RAM, etc. and what other security programs you might also have loading/running on startup ?
Ensure that only essential programs load on startup, media players are a big culprit and don't need to load at startup only when a media file is run.