The Tecnodec is designed to be used with Rega arms which are 237 mm or 9.33 inches long. The SME slot should allow enough space for adjustment for a SME arm.
I'm using a Tecnodec with a Roksan Tabriz, 240 mm or 9.45 inches long.
Where did you get the SME armboard for the Tecnodec? I would like to use mine with a SME M-2 10 inch arm.