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

t=int(input())
for _ in range(t):
    n=int(input())
    l=list(map(int,input().split()))
    maxi=max(l)
    start=l[0]
    f=0
    for i in range(1,n):
        if(l[i]!=start):
            f=1
            break
    if(f==0):
        print(-1)
    else:
        ans=-1
        for i in range(n):
            if(l[i]==maxi):
                if(i+1<n and l[i+1]!=maxi):
                    ans=i
                    break
                if(i-1>=0 and l[i-1]!=maxi):
                    ans=i
                    break
        print(ans+1)