Aside from the underlying chords that are played, is it imperative to start and end your melody on the same note within your piece to indicate a modal tone? if so can you still use all the notes in the scale you use up and down loosely and not lose the sound of your mode as long as you started and end on the note that indicates the mode you want to emphasize?
The tonic note of a scale is merely and only the MOST CHARACTERISTIC note of that scale. It does not have to sound in order for the scale to be discerned, as plenty of other notes in the scale serve to also delineate that scale.
Let's use an example from modern pop music: Hootie and the Blowfish. The singer's melodies are banal, uninteresting, naive, trivial, mostly BECAUSE they slam the tonic note so relentlessly.
Think of it this way: moving away from the tonic note creates tension, while moving toward the tonic note resolves tension. Western music, in both harmony and melody, is about creating then resolving tension. The melody can range FAR AFIELD from the ostensible tonic, without breaking the "mood" of the stated key. Whether it finds its way back or not doesn't really matter, in terms of the listener's perception of key or modality.
You don't have to start or end on the same note. But bear in mind that chord progressions and melodies work differently.
Every melody or set of chord progressions suggests the mode. This is important to understand.
Example with chords: if you play: II - V you know what I is.
Example with a melody: by using triads or fifths you can suggest a root without playing it. Especially if you use a M7. This also works the other way around, you can play in the key of C and suggest -for example- D minor, even if you use Dorian. Miles Davis' So What is a great example of this.