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

for _ in range(int(input())):
    n = int(input())
    arr = list(map(int,input().split()))
    f = True
    for i in range(n-1):
        if arr[i]!=arr[i+1]:
            f = False
    if f==True:
        print(-1)
    else:
        mex = max(arr)
        pos = -1
        for i in range(n):
            if arr[i]==mex:
                if i-1>=0 and arr[i-1]!=mex:
                    pos = i
                if i+1<n and arr[i+1]!=mex:
                    pos = i
        print(pos+1)