No point in heading to Cambodia from CM or Samui, but I presume you're arriving & departing via BKK, so if you have a spare few days (minimum) you could take a flight to PP, and from there take an Angkor tour. Air Asia have budget flights BKK - PP, so if interested you could check their website and try to schedule in a sidetrip to Cambodia.

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The Truly Wise Man Never Plays Leapfrog With A Unicorn