1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

from sys import stdin,stdout


ans = []
def main():
    n = int(stdin.readline())
    arr = list(map(int,stdin.readline().split()))
    maxval = max(arr)
    ind = -2

    for i in range(n):
        if arr[i] == maxval:
            if i > 0 and arr[i-1] != maxval: 
                ind = i
                break
            if i < n-1 and arr[i+1] != maxval:
                ind = i
                break
    
    ans.append(str(ind+1)) 


if __name__== '__main__':
    for i in range(int(stdin.readline())):
        main()

    stdout.write('\n'.join(ans))
